What kind of constipation is considered harmfull? i have stool everyday but i feel the quantity is little.

Time for evaluation?: Is this new for you? Have you had testing that distinguishes a "slow transit" system, or tests that suggest inflammation (like crohn's, ulcerative colitis), infection, stenosis (the narrow passage you mentioned), extrinsic impression against the gut, pregnancy, etc.? Do you have irritable bowel syndrome? Pelvic floor dysfunction? A medical evaluation is in order--please see your GI doctor.